On the market there are at present to be found several antennas and antenna system designs for the different application fields of radio transmission and reception, for example satellite communications, radar installations or mobile telephone networks. In this context antennas designed for base stations, for example serving mobile or handheld phones, are of particular interest and especially when using a microwave frequency range.
Present base stations with active antennas will usually have separate antennas for transmission and reception. For transmission there is normally one array antenna for each radio frequency channel, the reason for this being that single carrier power amplifiers (SCPA) can be made with a considerably higher efficiency than multi carrier power amplifiers (MCPA) due to the absence of intermodulation effects. Generally two separate array antennas are used for reception of all the different channels within a frequency range for obtaining diversity. The receive array antennas will be separated a number of wavelengths to reduce influence of fading (also referred to as space diversity). FIG. 1 demonstrates a typical antenna configuration for one sector having three carrier frequencies. All the individual array antennas, both for the reception and the transmission, are here presented as having equal size.
A document WO95/34102 discloses array antennas for utilization within a mobile radio communications system. This antenna comprises a microstrip antenna array with a matrix of microstrip patches having at least two columns and two rows. In addition a plurality of amplifiers will be provided wherein each power amplifier for transmission or each low noise amplifier for reception are connected to a different column of microstrip patches. Finally, beamformers are connected to each amplifier for determining the direction and the shape of narrow horizontal antenna lobes generated by the columns of microstrip patches.
Another document U.S. patent application Ser. No. 5,510,803 discloses a dual-polarization planar microwave antenna being based on a layered structure, the antenna having a fixed and unchangable utilization of the aperture. The antenna may be understood as two fixed, superimposed, single-polarized antennas.
A third document EP-A1-0 600 799 discloses an active antenna for variable polarization synthesis. The antenna, intended for radar applications, utilizes a hybrid coupler with a phasing control of one or two bits, which adds a dephasing of 0.degree., 90.degree. or 180.degree. permitting the synthetization of linear orthogonal polarization or circular polarization. It is presupposed that the antenna by means of switching may be utilized either for transmission or reception.
Still, in this field of applications, there is a desire and a demand to design and implement compact base station antenna devices and systems having a balanced link budget, for instance for mobile communications.